1. Field of the Invention
This invention relates to toner cartridges used in electronic or laser printers and more particularly to moving agitators for delivering toner from the cartridge's toner tank to its toner metering and delivery components.
2. Background Information
Electronic or “laser” printers use a focused light beam to expose discrete portions of an image transfer drum so that these portions attract printing toner. Toner is a mixture of pigment (typically carbon black or a non-black color component) and plastic. The toner becomes electrostatically attracted to exposed portions of the image transfer drum. As a transfer medium such as paper is passed over the rotating image transferred drum, some of the toner is laid onto the medium. Subsequently, the medium passes through a heated fuser so that the plastic is melted into permanent engagement with the underlying medium.
The vast majority of desktop laser printers currently available utilize replaceable toner cartridges that incorporate an image transfer drum, a toner tank and a metering system and a drive mechanism for the drum and metering system. A one-part toner is used, in which the fusible plastic and colorant (typically carbon black in a black-and-white system) are combined together. Modern toner cartridges often include a variety of sensors that interact with the laser printer in order to indicate the status of the cartridge. Indications relating to toner level, print quality and general cartridge function are often included. A large number of types and sizes of toner cartridges are currently available. Each cartridge is provided with its own set of operating parameters and toner fill limitations. Some limitations are enforced by electronics within the cartridge and print engine that are set by the manufacturer. For example various cartridges, such as those used in the printers available from Lexmark International, Inc. utilize a complex sensing system for determining cartridge performance and preventing cartridge from being filled in excess of the manufacturer's specifications.
The cartridge's sensing system includes an encoder or timing wheel interconnected with one end of a rotating agitator blade within a semi-cylindrical toner tank. Movement of the agitator blade feeds toner into the metering system. The timing wheel reports the movement of the agitator through the toner reservoir. The resulting signal must fall within certain parameters, or a variety of error conditions are indicated by the printer, and print engine operation may suddenly cease.
The timing wheel includes a set of perimeter notches at predetermined arcuate positions. The notches interact with an optical or electromechanical sensor on the print engine. The timing wheel is fixed to the agitator blade via a common shaft. Coaxially mounted on the shaft is a main drive gear that is operatively connected with, and synchronized to the print engine drive train (including the developer roll, image drum, etc.). The timing wheel and agitator blade shaft together provide “lost motion” or dwell (or “float”) with respect to the drive gear within a predetermined arcuate limit. In this manner the agitator is spring loaded and alternately dwells or snaps back against a spring stop as is passes through the toner load. If the toner load is too high, the dwell and snap back signals an overfill condition via the timing wheel. If the toner is too low, there is virtually no dwell/snapback, indicating an empty cartridge, both conditions will stop the print engine.
Commonly owned U.S. Pat. No. 6,510,303 B2, entitled EXTENDED-LIFE TONER CARTRIDGE FOR A LASER PRINTER, by Lionel C. Bessette, the teachings of which are expressly incorporated herein by reference, addresses certain problems encountered in providing a higher initial toner charge to a cartridge with strict sensing limitations on volume. In essence, the timing components are modified to allow wider/different range of dwell and snapback encountered with a higher initial toner level without causing the printer to stop. This teaching also provides for an enlarged cartridge volume via an attached extension. Likewise, commonly owned U.S. patent application Ser. No. 11/246,926, now U.S. Pat. No. 7,433,612 entitled TIMING WHEEL FOR TONER CARTRIDGE WITH DUAL SPRINGS, also by Lionel C. Bessette, the teachings of which are expressly incorporated herein by reference also solves certain timing problems encountered as the level of toner decreases as it is expended over time.
These teachings seek to address particular electronic limitations posed upon over-filled cartridges by the print engine. However, increasing the quantity of toner may also lead to certain physical limitations on performance. When the toner level/volume in a cartridge is increased, the agitator must work harder as it traverses the toner load. Agitators generally consist of a main axle shaft that engages the timing gear and the floating main drive gear. The shaft supports a series of radially projecting ribs along its axial length. These ribs are topped by a cross bar that is located close to the cylindrical inner wall of the toner tank. The cross bar acts to scoop the toner out of the tank and deposit it in the toner metering area, where it is deposited upon a magnetic developer roll, or conductive elastic roller leveled by a doctor blade and then selectively directed to the electostatically charged, photo-conductive image drum.
The cross bar is most useful when the toner level is relatively low and toner must be physically carried into the metering area from the bottom of the tank. At higher fill levels, the toner simply migrates by gravity into the metering area, and the cross bars merely “agitate” the load. Unfortunately, the higher the level, the greater the drag on the agitator, and hence, the print engine motor. Conversely, the cross bar must provide some standoff space with respect to the toner tank's inner wall to allow toner to flow around it, especially at higher fill levels, so as to prevent jams. This reduces its ability to scrape out and scoop up the last bits of toner when the cartridge is nearly empty. In essence, it is highly desirable to employ less agitation at higher fill levels, while more-aggressive scooping at lower fill levels would increase efficiency. The current agitator blade is a tradeoff between these two opposing goals.